This invention relates to an exposure apparatus and, more particularly, to an exposure apparatus used to manufacture a semiconductor device by exposing a resist on a substrate to a reticle pattern.
Examples of such exposure apparatus known in the art include a stepper which sequentially exposes a plurality of exposure areas on a substrate such as a wafer to a pattern on a reticle via a projecting optical system while the substrate is moved in steps, and a scanning-type exposure apparatus which moves a reticle and a substrate relative to a projecting optical system and scans the reticle and the substrate by slit-shaped exposing light to thereby expose the substrate to the pattern on the reticle by scanning.
A so-called step-and-scan-type exposure apparatus has been proposed in recent years. This apparatus exposes a plurality of areas on a substrate to a fine pattern in a highly accurate fashion by repeating the above-mentioned stepping motion and scanning exposure in such a manner that exposure of a fine pattern can be achieved with greater accuracy. This exposure apparatus is so adapted that the portion of the exposing light comparatively near the optical axis of the projecting optical system is extracted by a slit so that the substrate is exposed by the slit-shaped light. This makes possible the exposure of a fine pattern with improved accuracy.
When scanning exposure is performed in this exposure apparatus, a reticle stage or wafer stage must be moved while controlling position in a precise fashion. To accomplish this, the positions of these stages are monitored by laser interferometers. Further, in order to position a wafer at the focusing position of the projection optical system in this exposure apparatus, the position of the wafer surface is sensed by projecting measurement light onto the wafer using a projector and receiving reflected light from the wafer by a photodetector. Position can thus be sensed highly accurately in accordance with the method of measurement. However, the increasing miniaturization of semiconductor devices in recent years has been accompanied by the appearance of measurement error caused by variations in the temperature of the air along the optical path of measurement. This has led to the adoption of systems in which the temperature along the optical path of measurement is kept fixed by an air conditioner.
In such an exposure apparatus, however, the accuracy with which the positions of the reticle and wafer stages are measured and the accuracy with which the position of the wafer surface is measured are not satisfactory for the purpose of exposing fine patterns with greater precision. In addition, it is required that scanning exposure be started upon attenuation of vibration caused by acceleration and deceleration of the stages when they are moved. The state of the art is such that it takes considerable time for vibration to attenuate. This makes it difficult to improve productivity.